The present invention relates to an image signal processing equipment/apparatus for processing image signals which are different in their baseband signal format, such as a NTSC signal and a MUSE signal.
There has been proposed, as an image signal transmission system, a MUSE system which bandwidth-compressed a high definition television signal having 1125 scanning lines into a signal at about 8.1 MHz by means of multiple sub-Nyquist sampling processing. This transmission system, as disclosed in NHK GIJUTU KENKYU "DEVELOPMENT FOR THE MUSE SYSTEM" Vol. 39, No. 2, 1987, carries out the offset sub-Nyquist sampling between fields, between frames, and lines so that the sub-sampling phase makes a tour for four fields. Basically, a television receiver for high definition television broadcasting is only required to decode the above MUSE signal to restore a high definition television image. This receiver, however, is expected to be able to process the NTSC television broadcasting which is adopted at present. If this can be realized, the receiver becomes inexpensive and also its using value can be increased.
The prior art for this purpose is disclosed in
JP-A-62-206977 entitled "High Definition Digital Television Receiver". In the equipment, as shown in FIG. 2, a NTSC signal supplied to a NTSC signal input terminal 1 is supplied to both one terminal of a switch 2 and a NTSC signal processing circuit 3. The NTSC signal is selected by the switch 2 which is connected with the side indicated by a solid line, using a control signal from a control terminal to be sent to a first frame memory 5; this frame memory 5 and a second frame memory 6 which is in a cascade connection with the first frame memory 6 are adapted to be suitable for the NTSC signal processing by the control signal from a conductive line 41. The NTSC signal two frames before is supplied to the NTSC signal processing circuit 3 through a switch 7 to which the output from the second frame memory is supplied and is connected with the side indicated by a solid line, and a conductive line 71. Also, the NTSC signal one frame before is supplied to the NTSC signal processing circuit 3 through a conductive line 51. After having performed a predetermined processing, the NTSC signal processing circuit 3 sends out an image signal based on the NTSC signal to a first signal output terminal 10 as a first output signal.
On the other hand, in the case where a MUSE signal supplied to a MUSE signal input terminal is to be processed, the switches 2 and 7 are connected with the side indicated by a broken line which is opposite to the case mentioned above. Also, the first frame memory 5 and the second frame memory 6 are adapted to be suitable for the MUSE signal processing by the control signal from the conductive line 41. Thus, the MUSE signals are supplied to a MUSE signal processing circuit 9. After having performed a predetermined processing, the MUSE signal processing circuit 9 sends out to a second signal output terminal 80 a high definition television image signal which has been obtained by decoding a bandwidth-compressed signal.
The above prior art, however, has the following disadvantage. In the prior art, only the first and second frame memories 5 and 6 (having a memory capacity of about 4 Mbit, respectively) which are required in principle to process the MUSE signals are also used to process the NTSC signals; the other signal processing circuits are individually provided. Therefore, it is difficult to greatly reduce the production cost of the television receiver having the prior art. In order to realize this, the signal processing circuits are required to be considerably simplified.